Ultrasonic generators with an ultrasonic source and a resonator for emitting ultrasonic sound are known in the art. The ultrasonic generator is used for treating a medium, e.g. a fluid or a liquid with ultrasonic sound, in particular with low-frequency-power-ultrasonic oscillations. Usually, the medium is arranged in a receptacle, for instance in a conduit like a pipe, or a container like a beaker. In the container, the medium may be stationary and in the conduit, the medium may flow. Media are often provided in disposable receptacles when treating the media with ultrasonic sound.
Low-frequency-power-ultrasonic sound is ultrasonic sound with a working frequency between 15 and 100 kHz, preferable 15 to 60 kHz, for instance 26 kHz and an acoustic power above 5 W, preferable between 10 W and 32000 W, e.g. 200 W. For generating the ultrasonic sound, the ultrasonic source is e.g. a piezoelectric or magnetostrictive source. The resonator may be a sound transducer, converting the ultrasonic sound to ultrasonic oscillations. Media treated with ultrasonic sound are e.g. fluids, dispersions, emulsions, suspensions, pastes, paints, dyes, inks or nano materials. The media can have various viscosities between 0 mPa*s to 3*1010 mPa*s, preferably 0.1 to 1*106mPa*s, e.g. 200 mPa*s.
For ultrasonic treatment, the resonator may transmit oscillations with amplitudes between 1 to 350 μm, preferably 5 to 50 μm and e.g. 15 μm directly or indirectly to the media. Lambda is a wavelength that results from the ultrasonic frequency and a sound propagation velocity in the resonator. The resonator may comprise one or several lambda/2-elements. A resonator comprising several lambda/2-may be produced from one piece of material of an appropriate length or of several elements of a whole-number or of a whole-number multiple of 2, the elements being interconnected in an ultrasonic sound transmitting manner, e.g. by screwing, welding, bonding or pressing. Lambda/2-elements can comprise different material cross section geometries, e.g. circular, oval or rectangular cross-sections. The cross-section geometry of each of the lambda/2-elements may vary along a longitudinal axis of the respective lambda/2-element. Lamda/2-elements may be made of metallic or ceramic materials or of glass, in particular of titanium, titanium alloys, steel or steel alloys, aluminium or aluminium alloys and, e.g. of titanium grade 5 among others.
Media may be treated with ultrasonic sound in open systems, e.g. in the beaker. Some processes require introducing low-frequency-power-ultrasonic sound in reactor vessels. For instance medical or pharmaceutical applications require inexpensive receptacles, e.g. reactor vessels, which are disposed off after single use. In the receptacle, e.g. the reactor vessel, the medium may have a lower or a higher pressure compared to the ambient pressure. The higher pressure may be a pressure that is between ambient pressure and 1.000 bar, preferably between 1.1 bar and 4 bar, for instance 1.2 bar absolute.
In order to deliver the low-frequency-power-ultrasonic sound to the medium in the receptacle, a wall of the receptacle may be oscillated by the resonator that is pressed against an outer side of the wall. Alternatively, the resonator may be completely arranged inside the receptacle. In particular, the ultrasonic source may be arranged outside of the receptacle and the oscillations are conducted via one or several resonators into an internal space of the receptacle.
In order to effectively connect the wall of the receptacle to the ultrasonic resonator, the resonator is to be pressed onto or against the receptacle, e.g. the reactor vessel, which may have a soft or a rigid wall. Low-frequency-power-ultrasonic is a pressure sensitive technology. The inner pressure of the receptacle influences transmitting of ultrasonic sound. Furthermore, hydrodynamic forming of cavitation and other processes acting against the introduction and distribution of ultrasonic sound into the medium, for instance degassing, may effect the treatment.
In particular with receptacles having a soft wall, a sufficiently high inner pressure for creating a contact pressure between the receptacle and the resonator is often insufficient.